To be completely honest, I found living by myself really difficult at first. I'd only ever lived with my family, uni friends or my ex beforehand, so living alone for the first time at the age of 29 was a massive change. I was also really mentally unwell which definitely complicated things and made everything 10 times harder. But it's not so bad anymore and you do get used to it with time.
I'd say the most important thing is to try and plan things when you know you'll be at home, even if it's something small. You don't have to account for every minute of your day but having a rough schedule can keep you occupied and with a routine. I'm generally at home at the weekend so if I'm not seeing my friends or travelling to visit my parents, I go shopping, go for a walk, spend a lot of time reading in cafes, visit the local library, get on a train and go somewhere new, literally anything that gets me outside. Having some kind of human contact when I'm not at work is so important; isolating myself from everyone only made me more miserable.
Plus doing things by yourself will give you confidence and a sense of wellbeing, knowing that you don't need to constantly be around anyone else and can have a nice time on your own can do wonders for your mental growth.